It is fundamental that water is essential for the survival of most plants and animals. Potable water is also a resource that is finite is quantity and quality. Because of its widespread use as a human consumable and for supporting food growth it is vital that a steady supply of potable water continue to be available. Potable in this context means water of sufficiently high quality that it can be consumed or used with low risk of immediate or long term harm. While there certainly can be a wide variance in tolerances in different geographical locations, the basic requirements are the same everywhere, only the tolerance levels may change.
To achieve potable water from water that is outside the potable limits (whatever they may be for a given region) there are three things that must be accomplished. These are: removal of parasites; removal of hazardous chemicals; and removal of bacteria and viruses. Collectively, parasites, hazardous chemicals, bacteria and viruses can be thought of as contaminants. If all these contaminates are removed then the resultant water is pure. However, since humans can tolerate some levels of contaminants (in fact some parasites, bacteria and viruses may actually be helpful) it is not necessary that the levels be reduced to zero to have potable water. But the harmful ones must be reduced below the tolerance level for a given region.
Parasites removal requires filtration of water born solid to a level in the one micron range. Since the human eye does not see solids smaller than approximately 25 microns, and since the filtration process slows down water movement, a typical municipal system would filter down to the sub-25 micron level but not below 3-microns. Thus, parasites, such as cryptosporidium and giardia, can be found in municipal water.
Many hazardous chemicals do not respond to filtration. They are instead removed by absorption and adsorption. Absorption is an inside process while adsorption occurs on the outside of the combination of media (minerals) being used. For example, carbon would operate to absorb and adsorb hazardous chemicals. At a certain point when the media (carbon or other material) tank is full, it is discarded and a fresh media tank installed. But it is not filtration. The hazardous chemicals are typically water soluble and need to be grabbed. There are two factors involved in achieving the “grabbing”. One factor is to have a formula of various minerals, that in conjunction with each other work to absorb or adsorb the chemicals. The second factor is retention time, so that the chemicals in the water coming through have enough time to be “grabbed”, instead of being channeled through. One system for “grabbing” chemicals from water is the Global-LS3-Multi-Media-Treatment Process available from Global Water Group located in Dallas, Tex.
Bacteria and viruses are typically reduced by chlorine. However, chlorine is a hazardous chemical. The World Health Organization has been trying to stop the use of chlorine as a water cleaning agent because chlorine in water that has not been cleaned—and as above-noted most water is not cleaned—creates carcinogens. Some people estimate that a high percentage of cancer deaths stem from chlorine treated water. An alternative for killing bacteria and viruses in water is to expose the water to ultra-violet light.
One major problem in the treatment of wastewater is the creation of a byproduct called sludge. The sludge, by definition, contains the contaminants removed from the water. Wastewater sludge carries all the contaminants, hazardous metals, chemicals, etc. and today this sludge is dumped in a landfill. The contaminants then leach into the earth and find their way to aquifers, rivers and streams all over the world. Not a good situation.
In the offshore oil and gas business since there are no fields in which to dump the sludge they have designed systems using the concept of aerobics. These systems use organisms to eat the organic sludge. The residual, while cleaned substantially, is not perfectly free of contaminants. This residual is then chlorinated and then dumped. Since the residual is not perfectly clean, carcinogens are formed which are then spread about.
An activated sludge system is known. In such a system the water would first be exposed to aeration where particles are broken up and biologically reduced. Then the partially cleaned water goes through a clarifier and the sludge would be pumped back until most of it is reduced. The remaining sludge is then dumped. The process takes about 24 hours but still results in suspended solids and viruses.
Thus, the existing extended aeration-activated sludge systems take too long to process and do not yield potable water.